Polymerization of compounds containing a terminal methylene group



7 amaze ronmaarzarron'or comounns con- TAININ G GROUP A TERMINAL.METHYLENE I Bernard Thomas Dudley Sully, Ewell, England,

aasignor to A. Boake Bobertaand Company Limited, London, England, aBritish company in, Drawing. Application June 29, ms,

Serial No. sssso This invention relates to the polymerisation ofcompounds containing a terminal methylene group, such as methylmethacrylate, vinyl acetate, vinyl chloride, acrylonitrile, butadiene,monostyrene, homologues oi monostyrene, vinyl naphthalene and vinylnaphthalene homologues. This application is a continuation-impart of myapplication Serial No. 609,497, filed August 7, 1945, now abandoned.

In my co-pending application Serial No. 484,913, flied April 28, 1943,and now abondoned, I have described a process for the polymerization ofa monomeric vinyl material consisting essentially of monomeric styrene,comprising continuously agitating an aqueous dispersion 'of suchmaterial at a temperature above 60 C; and for a period of time of from 1to 24 hours in the simultaneous presence of (a) a water soluble salt ofan oxy-acid of sulphur which inwater absorbs free oxygen with resultingoxidation of its sulphur atom to a higher valency, said oxy-acid saltbeing selected from the group consisting of sulphites, bisulphites andhydrosulphites. free oxygen occupying a vapour space above thedispersion and supplied thereto at an hourly rate 9 Claims. (Cl.260-89J) maining ingredients of the dispersion, it having been foundthat the merest trace of. say, copp sulphate in the dispersion wills'uilice for the purposes of the reaction, particularly if the quantityof available oxygen present in the reaction sphere, and therefore therate of feed of oxygen thereto (since the oxygen becomes used up as fastas it is supplied to the reaction sphere) be kept very small in thesense indicated in my said prior of feed of from 0.0004-005 part byweight per 100 parts of monostyrene to be polymerised, and (c) asubstance acting tocatalyse the oxidation of the sulphur atom of theoxy-acid salt, said substance being a simple water soluble salt of ametal of the type known to catalyse the oxidation by gaseous oxygen ofsulphites in aqueous solution '(see, for instance, "A ComprehensiveTreatise on Physical and Inorganic Chemistry" by J, W.

, Mellor, vol 10, page 264, and Zeitschriftfiir Physikalische Chanie,1903, vol. 45, page '641).

The oiw-aeidsalt of sulphur used may; for example, be'anhydrous sodiumsulphite (NazSOs), anhydrous potamium sulphite (K2803), ammoniumsulpliite, sodium bisulphite, sodium hydrosmpmte (nalsloo, potassiummetabisulphite (KzSiOs) or acetone sodium 'bisulphite, the lastmentionedbeing formed, for example, in situ in the dispersion by adding acetoneand sodium bisul'phite-thereto;

The substance acting to catalyse the oxidation reaction may, forexample,be a water-soluble application Serial No. 484,913, for example'of theorder, as regards concentration, of 0.01% by volume of the vapour spaceabove the dispersion (i. e. in the reaction vessel), and as regards rateof feed, of 0.005-0.024 part by weight per 100 parts of monostyrene tobe polymerised.

With the use of such a process and particularly if a very small rate offeed of oxygen as referred to above and correspondingly slow rate ofoxidation be employed in the reaction, it is possible to producepolystyrene of an average molecular,

weight well above 100,000 (for example up to 500,000), with a high yield(e.- g. substantially complete polymerisation of the styrene) and in arelatively short polymerisation time (e. g. from 1 to5 hours), theproduct being capable, moreover, of easy purificatiton. These resultsare obtainable even when operating at relatively high temperatures, forxample temperatures upwards of say 75 C. and more usually just below theboiling point'of the dispersion (e. g. 90 O.)--a fact which isremarkable in view of h the well known tendency in the polymerisation ofstyrene, forhigh temperatures and catalysis to favour the production oflow average molecular weight poly- 544,458, filed July 11, 1944, andnowabandoned, I have described a similar pro'cessto that described inthe aforesaid applicatiton Serial N0.-.iiilifilli,

according to which, in place of 'a'water-soluble i salt of anoxy-acid'of' sulphurwhich in-water' abnarily obtained on the market, orthat may be fortuitously present in one or other of the resorbs freeoxygen with resulting oxidation of its sulphur atom to a higher valency,free sulphur dioxide is'employedL 'I have now-found as the result offurtherim' vestigation that the process, both in the form thereof usingan oxidisable sulphite as referred to and in the form using free sulphurdioxide, separately from or conjointly with the use of an oxidisablesulphite, is capable of-application, as

regards the starting material, to other compounds containing a terminalmethylene group (it being understood, of course. that monostyrene fallswithin the category of such compounds), for

example, the specific compounds of this type hereinbefore mentioned.

I have also found that excellent results are obtainable when, instead ofintroducing the necessary controlled quantity of oxygen (for theoxidation of the oxy-acid sulphur salt or sulphur dioxide employed) intothe dispersion indirectly, through the intermediary of a vapour spaceabove the despersion, it is introduced directly, preferably in one orother of the following forms:

(1) Pure oxygen gas in solution in water, the gas being dissolved in thewater to an extent which is based on the known solubility of oxygen inwater.

(2) Oxygen as air, in solution in water.

(3) Oxygen in nascent form, produced within the dispersion byelectrolytic action therein, using electrodes in contact with thedispersion.

I have further found that the necessary oxidation of the sulphur-oxygencompound can be achieved by way of chemical interaction in situ in thedispersion as between the sulphur-oxygen compound therein (oxy-acidsulphur salt or sulphur dioxide) and an oxygen-yielding compound such ashydrogen peroxide, ethyl benzene peroxide, benzoyl peroxide or tetralinhydroperoxide, also present in the dispersion, or as between thesulphur-oxygen compound therein (oxy-acid sulphur salt or sulphurdioxide) and a metal salt (e. g. CuSO4) reducible to a lower valency bysuch interaction.

My further tinvestigations have also shown that the direct method ofintroducing the oxygen into the dispersion by one or other of the three.

modes (1), (2), (3) set forth above, and also the methods just describedof achieving the necessary oxidation in the process are applicable tocompounds containing a terminal methylene group generally, including inparticular the speciflc compounds of this category hereinbeforementioned.

The method according to the present invention, of introducing thenecessary controlled amount of oxygen into the dispersion directly, andalso the methodreferred to of achieving the necessary oxidation of thesulphur-oxygen compound by interaction in situ in the dispersion asbetween the sulphur-oxygen compound therein and either anoxygen-yielding compound (e. g. a peroxide) or a metal salt capable ofbeing reduced to a lower valency as the result of the interaction, areadvantageous, more especially in the production of high averagemolecular weight products, for which, as already indicated, it isnecessary to establish and maintain a close control of the oxidation inthat with these methods the necessary close control is readilyestablishable and maintainable.

When efiecting the oxidation with the use of an oxygen-yielding compoundor a metal salt as referred to above, the quantity used of the compoundor salt would depend upon the required average molecular weight of thepolymer mixture to be obtained, since this in turn depends upon theoperating rate of oxidation in the process. The same would apply alsowhen any of the modes (1), (2), (3) of oxygen supply to the dispersionwas employed; the quantity of oxygen supplied would again depend on therequired average molecular weight of the polymer mixture to be obtained.Preliminary trial will always suffice to indicate the requisite quantityin any given case, although such quantity will in every case besuificiently restricted to limit the rate of oxidation of thesulphur-oxygen compound to a rate which is equivalent to that whichwould result from an hourly rate of feed of oxygen to the dispersion offrom 0.0004-0.05 part by weight per parts of monostyrene to bepolymerised as in the processes of the applications Serial No. 484,913and Serial No. 544,658 aforesaid, and the total oxidation in thepolymerisation to a figure equivalent to a total oxygen consumption inthe process not in excess of 0.1 and usually between 0.1 and 0.01, partby weight of oxygen per 100 parts of material submitted topolymerisation, again as in the processes of said applications SerialNo. 484,913 and Serial No. 544,458, conditions which would result incessation of oxidation of the sulphur-oxygen compound having always tobe avoided, at any rate for any extended period in the course of thereaction.

As is also true of the processes of the earlier applications referred toin the preceding paragraph, the pH of the aqueous medium of thedispersion is a factor of importance, more especially for the successfulproduction of high average molecular weight products. It is preferablybetween pH 8 and pH 10 when the catalyst used in the process is a saltof copper, whereas when a salt of iron is employed the pH is preferablyon the acid side of strict neutrality.

The sulphur-oxygen compound used in the process of the present inventionmay be any of the oxy-acid sulphur salts mentioned above as used in theprocess of the earlier application Serial No. 484,913, or alternativelyfree sulphur dioxide (S02 gas) as used in the process of the earlierapplication Serial No. 544,458. In short, it may be any sulphur-oxygencompound normally having reducing properties and susceptible tooxidation by dissolved oxygen in an aqueous medium. In a similar way thecatalyst used to promote the oxidation of the sulphur-oxygen compound,or as the case may be the metal salt used to effect the oxidation byinteraction with the sulphur-oxygen compound, may be any of thepolyvalent metal salts mentioned in the earlier applications Serial No.484,913 and Serial No. 544,458, that is to say, practically anywatersoluble salt of copper, manganese, iron, cobalt, chromium,provided, in the case where the salt is used to efiect the oxidation byinteraction with the sulphur-oxygen compound, it is one which isreducible to a lower valency by the interaction, and it may be eitheradded as such to the dispersion or in the case where it acts in thecapacity of a catalyst to promote the oxidation of the sulphur-oxygencompound, constituted at least in part by the commoner metallicimpurities present in the sulphur-oxygen compound and/or the otheringredients used to form the dispersion.

For the purposes of a close control of the oxidising and polymerisingconditions in carrying the process of th present invention into effect,it is frequently advantageousor necessary, as in the case of theprocesses described in the earlier applications, to remove from thematerial to be polymerised-any free oxygen or peroxidic substance thatmay be contained in it prior to its dispersion in the aqueous medium,and similarly to remove any free oxygen that may be present in theaqueous vehicle of the dispersion or in any of the materials dissolvedor dispersed therein other than the material to be polymerised.

Also it is generally desirable for considerations of manufacture and forthe production of products of relatively higher average molecularweight, again as in the processes of the earlier applications, to employa starting material which has been freshly distilled or otherwisepurified prior to use, for example, by one or other of the methodsdisclosed in the earlier applications. Aged styrene, for example, whichhas not been carefully purified and freshly distilled, may possess aninitial inhibition period for as long as several hours, which in somecases may be so prolonged that the oxidation of the sulphite or othersulphur-oxygen compound employed reaches the stage of completion beforepolymerisation to any extent begins. In this connection,- it may beremarked that one of the desirable effects of the presence of acatalytic substance (e. g. copper sulphate) in the dispersion is toreduce any period of. inhibition that may tend to obtain, particularlyin a case where an emulsion stabiliser, e. g. gelatine, is Present inthe dispersion.

An emulsifying agentmay be used in the process, again as in theprocesses of the earlier applications, the substance selected for thispurpose varying with the sulphur-oxygen compound employed. For example,where a neutral or alkaline sulphite is employed, the emulsifier usedmay be a sodium, potassium or ammonium soap. Where on the other hand, anacid sulphite is employed, the emulsifier used may be a sulphonate of ahigher alcohol such as lauryl sulphonate.

A protective colloid may also be used for stabilising the dispersionduring the polymerisation, again as in the processes of the earlierapplications, suitable substances for this purpose including, forexample, gelatine, methyl cellulose, polyvinyl alcohol, saponin and gumarabic. In such cases, the action of the catalyst is, in general, sloweddown and accordingly 9. larger amount of the catalyst has to be employedfor an eflicient polymerisation than would be required otherwise.

It is possible to employ as the starting material in the process, againas in the processes of the earlier applications, monostyrene or ahomologue thereof containing a diluent ingredient, for example ethylbenzene, without prejudice to successful polymerisation.

The amount of available S02 in the dispersion at the commencement of thereaction should in general be of the order of 0.1 to 2.5% reckoned uponthe total weight of the dispersionassum ing a monomer concentrationthereof of the order of 20-40% by weight, an optimum amount for ,,mostcases being in the neighbourhood of 0.5%. Any excess used over theamount'which is actually consumed in the polymerisation has to beremoved from the product by washing (e. g. with distilled water) and asthis involves additional expense, it is desirable to avoid it as far aspossible by the use of correctly determined amounts in making up thedispersion. The whole quantity need not be present initially; part maybe added during the course of the polymerisation.

The results obtained in the process are generally improved when thecompound to be polymerised is added to a solution of the rest of thesolids of the dispersion, being run thereinto continuously ordiscontinuously at a controlled rate, and while the solutionis beingefficiently stirred. The concentration of the dispersion in respect ofcompound to be polymerised should generally be such as to give aconcentration of solids as polymer in the final (polymerised) dispersionof from -40% reckoned on the total weight of the dispersion.

Example 1 A mixture of grammes of distilled water,

0.25 gramme of anhydrous sodium sulphite (NaaSOa) and 0.4 gramme ofsodium bisulphite (NaHSOalrOJ cc. of N/10 copper sulphate solution washeated to 70 C. and into it, while stirring, methyl methacrylate was runat an average rate of about 1 cc. per minute until 50 ccs. had

but with no other control of its supply or access to the aqueous bath.Polymerisation was complete in about half an hour.

Example 2 A mixture of grammes of distilled water, 100 grammes of methylmethacrylate, 10 ccs. of a 10% aqueous solution of'acetone bisulphitehaving a pH of 6.0 and 0.2 cc. of N/10 copper sulphate solution washeated to 50 C. with continuous stirring. Polymerisation was complete in15 hours, the polymethyl methacrylate which separated from the mixturewas obtained in substantially 100% yield and had an average molecularweight of 170,000 as determined by the Staudinger viscosity method,using the constant 1.8 10- and a concentration of 0.01 basal molecule ofthe polymer in benzene. It is to be noted that the temperature of thedispersion was lower than that for Example-1; also, the amount ofgaseous oxygen present was more limited.

Example 3 The conditions, in this example were the same as those inExample 2 with the exception that the operating-temperature wasincreased to 60 0. Complete polymerisation was obtained in 3 hours andthe polymerisation product had an average molecular weight ,of 65,000.The reduction in'the average molecular weight was due in part tooperating at a higher temperature than in Example 2.

Example 4 a slow stream of commercial nitrogen containing about 0.1%oxygen. Polymerisation was complete in about 15 hours and the producthad an average molecular weight of 157,000.

Example 5 200 ccs. of a 1% aqueous sodium sulphite solution and 0.5 cc.of a mixed M/10 CuSO4-M/5 M11804 solution was warmed to 50 C. withagitation in the presence of air admitted to the surface of the aqueousmedium of the dispersion. On running in vinyl acetate with continuedagitation in the presence of air, a rapid polymerisation was obtained.

Example 6 This example, which is in two parts (a), (b),

76 is a further example illustrating the use of free sulphur dioxide inthe process in place of an oxidisable sulphite and demonstrates that amere trace of oxygen in the system will sulllce to ensure an effectivepolymerisation. i

Part (a) .-80 grammes of freshly distilled monostyrene, 160 grammes ofdistilled water, 0.5 gramme of sulphonated lauryl alcohol, 0.2 gramme ofsulphur dioxide and 0.1 cc. of a N/ copper sulphate (CuSOa) solutionwere stirred at 93.0 0. (not quite refluxing) for 5 hours. During thisperiod a slow currentof commercial nitrogen containing 0.1% by volume ofoxygen was passed over the surface of the emulsion. The rate of now ofthe gas averaged 20 cos. per minute and corresponded to a total oxygenconsumption by the styrene material of about 6 ccsrduring the course ofthe polymerisation. All the styrene was converted to polymer and theaverage molecular weight of the product was 495,000.

the vapour space above the mixture had been flushed out with purenitrogen. At the end of the five hours the polymer content of theproduct, as determined by the methanol extraction method, was 12.3% andthe average molecular weight was Example 7 75 grammes of pure (1. e.freshly distilled) monostyrene, 150 grammes of distilled water, 9 cos.of 0.5 mol. commercial acid sodium sulphite (NaI-ISOa) and 0.9 gramme ofsulphonated lauryl alcohol were mixed with stirring, in a closed vesselimmersed in a thermostatic bath at 90 C. and connected to an airreservoir. Emulsification occurredimmediately and the emulsion had a pHof about 4. At the end of: about 9 hours powmerisation was complete. Thepolystyrene obtained had a specific viscosity of 0.725, equivalent to anaverage molecular weight of 403,000. Under the conditions of thisexperiment some free sulphur dioxide was evolvedin the dispersion fromthe sulphite therein.

Example 8 This example illustrates the case where the necessary oxygenfor oxidation of the sulphuroxygen compound is supplied to thedispersion in the form of a solution of air in water.

The following mixture was prepared in a closed flask with mechanicalstirring at a temperature of 90 0., adding the components in the ordergiven:

Sodium sulphite crystals (NaaSOa.'lHaO) gms 6 Stearic acid gms 3 Sodiumborate grm 0.6 Copper sulphate grm 0.0014

' Distilled water mls 3'75 The sodium borate was added to maintain thealkalinity of the emulsion and to increase its stability. The coppersulphate was added to the water before the addition of the otheringredients and served to catalyse the oxidationof the sulphite with theoxygen. '75 mls. of pure monomeric styrene was then added and waspolymerised in approximately 90 minutes. after at intervals ofapproximately half an hour 25 mls. of distilled water saturated with airand There- 25 mls. of distilled styrene were added. The required slowoxidation of the sodium sulphite in the presence of a trace of copperwas continued in this manner until 200 mls. of styrene and 125 mls. ofair saturated water had been added. If no air-saturated water had beenadded then the polymerisation would have stopped after the firstaddition of styrene had been polymerised.

The initial polymerisation was due to the air l0 which was fortuitouslycontained in the ingredients, together with the oxidising action of thetrace of copper sulphate used as the initial catalyst. The molecularweight of the product obtained in this way, after coagulation withhydrochloric acid and washing free from salts with distilled water, was519,000.

Example 9 lIhe polymerising bath employed in this example had thefollowing composition:

Sodium metabisulphite (Na2S20s) gms.. 1.50 sulphonated petroleum gms 2.0Distilled water mls 200 after 2 hours to maintain the emulsion in astable condition. The completely polymerised emulsion was coagulated bythe addition of hydrochloric acid. After washing, filtering and drying,the

resulting polystyrene had a molecular weight greater than 100,000.

Example 10 This example illustrates a variation of the method in whichthe slow oxidation of the sodium sulphite is caused by the passage of anelectrir current in a manner calculated to oxidise an amount of thesulphite equivalent to that oxidised by the air in the first example.

Sodium sulphite (anhydrous) gms 3 Stearic acid gms 1.2 Distilled water(oxygen free) mls 600 Caustic soda (4% solution) mls 1.2

The mixture was stirred for half an hour at a temperature of 90 C. and acurrent of 20 milliamperes was passed through the solution. Distilledstyrene (120 mls.) was then added. A sample of the emulsion taken after5 hours 65 showed that the polymerisation was complete.

The time of reaction, the temperature of operation and the productobtained are similar to those in the first example in which the sodiumsulphite is oxidised with oxygen dissolved in water. In an eificientpolymerisation it is not normally necessary to oxidise more than onefifth of the sulphite used and the passage of the current may beconveniently made intermittent. Copper electrodes may be used, in whichcase no added copper catalyst is necessary.

The molecular weights given herein are as determined by the Staudingerformula, which is as follows:

C is the concentration of polymer expressed .as basal mols, per litreand Km=1.8X (Staudingers constant), using in the tests a concentrationof 0.01 basal mol. of the polymer in benzene.

It will be appreciated of course that for the purposes of obtainingreproducible results, more especially as regards average molecularweight, it is advisable and usually necessar to employ a knownpredetermined amount of the substance acting to catalyse the oxidationof the sulphuroxygen compound during the course of the polymerization,for which reason it is generally necessary to add furtherquantities ofsaid substance over and above any quantity that may be providedfortuitously by the metallic impurities present in the sulphur-oxygencompound and/or other constituents of the polymerisation mixture. Inthis connection it may be remarked that although the merest traces onlyof such metals as copper iron, manganese, chromium or cobalt willfunction in the catalyst system of the invention, the rate ofpolymerisation and the average molecular weight of the polymers obtainedare to a considerable extent dependent upon the quanand thepolymerizable compound, having a tertity of metal in the catalystsystem, with the traces 01' such metal, as when depending upon themetallic impurities in the ingredients of the dispersion, any variationsin the quantity of metal present (which variations will be unavoidablewhen the metal is constituted solely by the metallic impurities referredto) tend to interfere with reproducibility and predeterminability of theproduct of the process, particularly in respect of average molecularweight. By increasing, however, the quantity of metal present in thesystem, by adding a further quantity to that already present in the formof metallic impurities, the resultant effect upon the product of thepolymerisation of small variations in the quantity of metal in thesystem is correspondingly reduced, with the result thatpredeterminability and reproducibility of the product are readilyobtainable.

Without binding myself to any expressed theory as to the mechanism ofthe polymerisation reaction which takes place in my process, I havereason to believe that the polymerisation of a monomeric polymerizablecompound having a terminal methylene group in an aqueous emulsion of asulphite or of sulphur dioxide is initiated by the formation ofmonothionic acid or an ion of monothionic acid (HSO: or .SOr) which hasthe property of a free radical. Monothionic acid has never been isolatedbecause as is usual with free radicals two molecules combine together toform dithionic acid (HzSzOs), a known acid whose salts can be isolatedin the pure state. It is known that monothionic acid free radicals ormonothionic acid free radical ions are formed in the aqueous sulphitesolutions by the presence of a minute amount of metallic impurity, asfor example a trace of copper. In

the process of the formation of a monothionic acid free radical or a'monothionic acid free radical ion the metal catalyst present in a traceonly is reduced to a lower state of oxidation in which state it is nologner capable of producing any more radicals. This isthe acceptedtheory for the function of copper in the oxidation of sulphitesolutions. For example:

Cu(OH) a-I-NazSOa =CuOH+NaOH+NaSOs If, now, an excess of gaseous oxygenis present minal methylene group the monothionic radicals preferentiallyactivate the eiflcient oxidation of the sulphite in the known mannerwithout the simultaneous polymerisation of said polymerizable compound.On the other hand, when anexcess of oxygen is avoided by restriction orcontrol, the monothionic acid radical or radical ion is caused tocombine with the said polymerisable compound with the formation of aradical of the said compound which serves as the starting point for amore effective chain reaction resulting in the formation of polymer inaccordance with the free radical theory of polymer formation. Thus, itis believed that the true function of the oxygen in the process is tooxidise the metallic catalyst back to the higher valency form so that bycombination with the sulphite ion or sulphur dioxide present it can onceagain lead to the formation of a monothionic acid radical or radicalion.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

l. A process for the polymerization in aqueous dispersion ofpolymerizable compounds containinga terminal methylene group whichcomprises heating the dispersion for a period of time of from 1 to 24hours in the presence of (a) a sulphur compound selected from the groupconsisting of'sulphites and free sulphur dioxide, said sulphur compoundbeing dissolved in the aqueous phase of the dispersion; (b) oxygen tooxidise the oxidation; and controlling the concentration of the oxygenavailable within the reaction sphere by carrying out the reaction in aclosed space, and supplying an hourly rate of feed from 0.0004 to 0.05part by weight of oxygen per' parts by weight of the compound to bepolymerized.

2. A process for the polymerization in aqueous dispersion ofpolymerizable compounds containing a terminal methylene group whichcomprises heating the dispersion for a period of time of from 1 to 24hours in the presence of: (a) a sulphur compound selected from the groupconsisting of sulphites and free sulphur dioxide, said sulphur compoundbeing dissolved in the aqueous phase of the dispersion; (b) oxygen tooxidise the sulphur compound introduced into the aqueous phase in-theform of an aqueous solution of molecular oxygen; and (c) a salt selectedfrom the class of metal salts that catalyse sulphite oxidation; andcontrolling the concentration of the oxygen available within thereaction sphere by carrying. out the reaction in a closed space, andsupplying an hourly rate of feed of from 0.0004

to 0.05 part by weight of oxygen per 100 parts by weight of the compoundto be polymerized.

I 3. A process for the polymerization in aqueous dispersion ofpolymerizable compounds containing a terminal methylene group whichcomprises heating the dispersion for a period of time of from 1 to 24hours in the presence of: (a) a sulphur compound selected from the groupconsisting of sulphites and free sulphur dioxide, said sulphurcompoundbeing dissolved in the aqueous phase of the dispersion; (b)oxygen to oxidise the sulphur compound introduced into the aqueous phaseas nascent oxygen produced in situ within the-dispersion by electrolyticaction; and (c) a salt selected from the class of metal salts thatcatalyse sulphite oxidation; and controlling the concentration of theoxygen available within the 11 reaction sphere by carrying out thereaction in a closed space, and supplying an hourly rate of feed of from0.0004 to 0.05 part by weight of oxygen per 100 parts by weight of thecompound to be polymerized.

4. A process for the polymerization in aqueous dispersion ofpolymerizable compounds containing a terminal methylene group whichcomprises heating the dispersion for a period of time of from 1 to 24hours in the presence of: (a) a sulphur compound selected from the groupconsisting oi sulphites and free sulphur dioxide, said sulphur compoundbeing dissolved in the aqueous phase of the dispersion; (1)) oxygen tooxidise the sulphur compound introduced into the aqueous phase asnascent oxygen produced in situ in the dispersion by chemicalinteraction therein between the sulphur compound in the dispersion andan oxygen-yielding substance also present therein with resultingoxidation of the sulphur compound; and (c) a salt selected from theclass or metal salts that catalyse sulphite oxidation: and controllingthe concentration of the oxygen available within the reaction sphere bycarrying out the reaction in a closed space, and supplying an hourlyrate of feed of from 0.0004 to 0.05 part by weight of oxygen per 100parts by weight of y the compound to be polymerized.

'5. A process as claimed in claim 1, wherein the reaction is carried outat a temperature of 90 C.

6. A process as claimed in claim 1, wherein the sulphite is sodiumsulphite and the metal salt is a copper salt.

7. A process as claimed in claim 1, wherein the polymerizable compoundis vinyl acetate.

8 A process as claimed in claim 1, wherein the polymerizable compound isvinyl chloride.

9. A process as claimed in claim 1, wherein the polymerizablematerial isstyrene.

BERNARD THOMAS DUDLEY SULLY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,356,925 Fryling Aug. 29, 19442,379,431 Fryling July 3, 1945 2,383,055 Fryling Aug. 21 1945

1. A PROCESS FOR THE POLYMERIZATION IN AQUEOUS DISPERSION OFPOLYMERIZABLE COMPOUNDS CONTAINING A TERMINAL METHYLENE GROUP WHICHCOMPRISES HEATING THE DISPERSION FOR A PERIOD OF TIME OF FROM 1 TO 24HOURS IN THE PRESENCE OF: (A) A SULPHUR COMPOUND SELECTED FROM THE GROUPCONSISTING OF SULPHITES AND FREE SULPHUR DIOXIDE, SAID SULPHUR COMPOUNDBEING DISSOLVED IN THE AQUEOUS PHASE OF THE DISPERSION; (B) OXYGEN TOOXIDISE THE SULPHUR COMPOUND; AND (C) A SALT SELECTED FROM THE CLASS OFMETAL SALTS THAT CATALYSE SULPHITE OXIDATION; AND CONTROLLING THECONCENTRATION OF THE OXYGEN AVAILABE WITHIN THE REACTION SPHERE BYCARRYING OUT THE REACTION IN A CLOSED SPACE, AND SUPPLYING AN HOURLYRATE OF FEED FROM 0.0004 TO 0.05 PART BY WEIGHT OF OXYGEN PER 100 PARTSBY WEIGHT OF THE COMPOUND TO BE PLYMERIZED.